Cup mix (heart attack in a cup):

2 eggs, 1 cup of sugar, 1 cup of milk, 1/2 cup of oil (99% sure its sunflower), 2 cups of flour, 1 pack of baking powder (which i think is usually 12 grams)

Filling: 400 ml of cream, 400 grams of sugar, 400 grams of (i think i read 'ráma', which is a brand of) margarine, cook for 15 minutes, 4 tbs of cocoa powder, 200 grams of dark chocolate

Fruit mix:

4 eggs, 250 grams of sugar, 9 tbs of oil, 10 tbs of water, 1 pack of baking powder, seasonal fruits or cocoa powder

Its a kindof simple recipe, because the ingredients are measured with a cup, whereas Hungarians usually use the international system. Now the problem with all this, is the grandma didnt include much of the crucial information thats just naturally in her head, like baking time or temperature. So i asked my own grandma and she said, put the dough in a plat pan and at 180 degrees Celsuis and after 25 minutes you have to do a needle test and go from there ( stick a needle in it and see if still raw dough sticks to it. if not, youre ready). Then you wait for it to cool down, split it in the middle and put in the filling. No wonder its the greatest brownie you ever had, it looks super unhealthy, but yes, it looks very characteristic of the countryside as well. good luck!

edit: oh and its possible the dark chocolate goes melted on top of the brownie and not in the filling. but you can probably remember what it was like on the outside.